FIG. 1 illustrates a cross section of a typical integrated circuit power transistor 100. A plurality of power transistors provides a “Christmas tree” structure of a “snake curving” structure. An examination of where the current flows and where it does not flow shows that the current flow is mainly confined to the outer edge of the emitter/base. This is due to the biasing of the emitter base 102. Voltage applied to the emitter base (Va) leads of the transistor result in this voltage Va appearing at the very edge noted as point “X. This results in a current flowing in the emitter edge (Ie) across the base to the collector with a small percentage of the emitter current flowing in the base lead (1−alpha times the emitter current, where alpha is almost 1) and resulting in current in the collector of almost all the Ie.
A small distance inwards from the edge of the base, the applied voltage is lower than Va due to the slight current flow in the base flowing across a very high resistance due to the pinching effect of the very thin base region. As one moves a little further under the emitter base junction from the edge, the voltage drop is a little higher and the voltage is now Va minus some additional millivolts of drop, therefore biasing this portion of the emitter base junction lower. The resultant emitter current injected drops dramatically at these points located inwards from the emitter base edge. For example, the current will drop as much as a decade for every 60 mv of drop. Therefore just a short distance in from the edge of the emitter base junction, the current flow is very low; i.e. most of the current is flowing at the edge of the emitter base. FIG. 2 is meant to show that only a small portion of the emitter base 102 is contributing to emitter current that can be collected by the collector. In essence, the cross-section of the transistor shown in FIG. 1 results in current flow that is pictured in FIG. 2. It is obvious from this representative figure that most of the emitter base is not participating in the active current of the emitter and the collector and its resultant beta (gain of the bipolar transistor). Most of the emitter base junction is wasted space.
What is desired is to allow the inactive portion of the emitter base to be put to better use and therefore result in significant saving of space among its attributes.
The present invention addresses such a need.